) 



33 



the neck of the plant (collet,) about a quarter of an inch 

 below the point where the leaves join the stem. If slices of 

 the neck be placed under the microscope in the early stage of 

 the injury, the sap vessels are found simply ruptured ; while if 

 the plant has been some time affected, as shown by its foliage, 

 a dark spot will be seen in the centre of the stem, and the more 

 external parts of a brown colour ; and as the disease spreads 

 upwards, the leaves and stem become black in their entire 

 thickness, decomposition takes place, and the plant rots away 

 a little below the base of the leaves. This destruction of the 

 cellular tissue is owing to the severity of the frost ; and if the 

 common cauliflower, or the celery plant, at the same period 

 of the year, be examined, the same effects will be visible. 

 In the cauliflower, about three inches below the leaves, the 

 centre of the stalk is found in its early stage, simply softened ; 

 afterwards it assumes a brown colour, and emits, if broken, a 

 putrid smell, decomposition having taken place. In the 

 celery plant the neck becomes filled with a brown sap, and 

 the blanched leaves soon take on the appearance of frost- 

 bitten celery. The first external symptom of the disease in 

 all the plants is a dead appearance of the edges of the leaves ; 

 which takes place first in those most developed, while the 

 leaves recently expanding seem healthy; but subsequently the 

 whole plant above the neck becomes of a dark colour, and, if 

 pulled, breaks off, leaving the lower portion of the roots 

 healthy in appearance. There is no doubt that the disease 

 is immediately caused by the sap of the plant becoming 

 frozen, and the air which is contained in it expelled among 

 the sap vessels. The heat of the sun then expanding the 

 confined air, before the re-absorption of it by the frozen sap 

 can take place, bursts the vessels of the plant. This is proved 

 by the fact that any frosted plant may be preserved if it be 

 gradually thawed, by either pouring cold water upon it, or by 

 protecting it from the sun's rays. Several hundred plants of 



VOL. II, 



D 



